Objectives: The aim of this study was to evaluate the procalcitonin (PCT) changes in two different high-dose colistin regimens in the treatment of multi-drug resistant MDR gram negative infections in ICU patients.

Method: This is a prospective study of adult ICU patients with bacteremia and ventilator associated pneumonia (VAP) caused by MDR gram negative pathogens. Patients were assigned to two colistin administration groups. Group A received 9 and group B received 3 million international units every 24 and 8 hours respectively. Baseline characteristics and measurements of PCT concentrations at the start, the 3rd and the 5th day of the antibiotic therapy and their trends between the two groups were recorded and compared.

Results: Of 40 patients enrolled, 34 completed the study protocol, of whom 30 (88.2%) had VAP and 4 (11.8%) had bacteremia. There were no statistically significant differences in the baseline characteristics between the two groups. The mean PCT levels in two study groups were; 2.34, 1.24 and 0.95 in group A and 5.89, 1.24 and 0.8 in group B at the baseline, 3rd and 5th day of colistin administration respectively (P=0.47). The ICU length of stay (LOS) in days and ICU mortality were; 31.31, 35.3% and 32.06, 22.2% in groups A and B (P=0.39, 0.87), respectively.

Conclusion: We did not find any statistically significant differences in the serum PCT levels, ICU LOS or ICU mortality, between the two groups, who received maximum recommended dose of CMS with 2 different intervals of every 8 or 24 hours.